This invention relates to fluid suction and discharge apparatus which are used for such as refrigerant compressors, and, more particularly, to improvements of such apparatus of a type in which pistons are reciprocated in respective cylinders by a wobble plate driven by a wedge-shaped rotor which is secured on a drive shaft.
Such a fluid suction and discharge apparatus having pistons reciprocated by means of a wobble plate and wedge-shaped rotor, are known as described, for example, by the refrigerant compressors disclosed in U.S. Pat. Nos. 3,552,886 (which is reissued under No. 27,844), 3,761,202 and 3,838,942. The fluid suction and discharge apparatus is little in volume and is suitable for refrigeration systems of the automotive or mobile type.
One problem in such a fluid suction and discharge apparatus is that vibration develops in greater degree than in apparatus of the other types.
Vibration of the apparatus is transmitted to any device (for example, a motor of a vehicle, the body of a car or other) on which the apparatus is mounted through mounting members so that bolts used in the apparatus and the device may be loosened, and the used parts may be damaged and their life times shortened.
The main reason why the fluid suction and discharge apparatus of this type develops vibration to a greater degree is thought to be that the wedge-shaped rotor is asymmetric about the rotating central axis thereof, and that, in operation, various motions of parts thereof are carried out. But the reason has not yet been fully resolved.
Even if the wedge-shaped rotor is formed hollow so that the centroid thereof may be on the rotating axis thereof as shown in the drawing annexed to above described U.S. Pat. No. 3,552,886, a considerable vibration still develops during the operation, although vibration is reduced to a certain degree.
If a system of the rotor, wobble plate, piston rods and pistons is so formed that a centroid of the system may be on the rotating axis of the drive shaft, vibration is more reduced, but the reduction of vibration is not yet satisfied.
The present inventor dynamically analyzed the system of the rotor, wobble plate, piston rods, and pistons (which system will be referred as "the operation system") and obtained the following conclusion;
1. If the centroid of the operation system is on the rotating axis, a centrifugal force uniformly develops around the rotating axis in the operation system so that no unbalanced radial force may exist. Accordingly, the radial vibration of the system does not occur.
2. During reciprocating motion of the pistons and piston rods, axial forces due to inertia thereof develop. But the sum total of the axial forces may be zero if all of the pistons and piston rods are equal angularly spaced around the rotating axis and if all the pistons and piston rods are equal to one another in mass. In this case, the system is not axially vibrated.
3. But the axial forces due to the inertia of the pistons and piston rods apply on different points on the wobble plate, and, therefore, provide a torque to the wobble plate on an axis perpendicular to the rotating axis.
Thus, the operation system is vibrated by this torque.
4. If the rotor is not so formed that the mass distribution thereof is symmetrical in relation to the rotating axis, a torque develops due to centrifugal forces during the rotation of the rotor, which rotates the rotor on an axis perpendicular to the rotating axis.
Accordingly, for the reduction of vibration of a fluid suction and discharge apparatus of a type in which a wedge-shaped rotor and a wobble plate are used for the reciprocating motions of a plurality of pistons and piston rods, torques as described in paragraphs numbered 3 and 4 are necessary to be suppressed. In addition, the operation system is so formed that the centroid thereof may be on the rotating axis.